The invention relates to optical railway signals and in particular to those of the type called "searchlight signals" where a disk mask has at the center a circular window from which one or more sources of light, associated to a suitable optical unit, project, selectively on the basis of a control, one of a plurality of colored lights, usually red, green and yellow.
In the oldest types of railway light signals, of the above specified type, there is provided a single light source or lamp with a respective optical unit which guides and projects a light beam through the window. Suitable chromatic filters are interposed between the lamp and the optical unit, and the colors are changed by shifting the filters by mechanical means, electro-magnetically operated.
With the purpose of avoiding movable parts (which are more prone to failure) static signals have been introduced having a number of light sources corresponding to that of the signal colors desired. In this case the device comprises, for each light source, an optical projector, which collects and projects a light beam emitted by the corresponding source, and this beam is taken in a respective light conducting system, or optical channel or guide, which directs it to the signal exit window. The optical unit associated to each light source comprises also the respective chromatic filter, which is obviously fixed. The light conducting system, or optical channel, consists of distinct bundles of optical fibers which, starting from each respective light source, are brought to converge into a single bundle, the terminal of which is operatively aligned with the signal window. A traffic signal of this type is described, for example, in my pending U.S. application Ser. No. 133,104 filed on Mar. 24, 1980 (now allowed).
Although the traffic signals of the type above disclosed have given satisfactory results, they present an inconvenience which is due to the fact that it is not possible to utilize the light conducting system, in correspondence of its terminal at the signal window, at the maximum of its capacity.
In fact, in the case of a light conducting system consisting of bundles of optical fibers, it appears evident that the single common bundle terminating in correspondence of the signal window consists of the union of three separate bundles (if three colors are required), and that therefore only a fraction of this common bundle (in the specific case 1/3) is actually used for the conveyance of the colored light.
According to the present invention, there is proposed a traffic signal which fully utilizes the light conducting system, or optical channel, also in its terminal portion associated to the signal window, thus obtaining an intensity of light for the irradiated colored light beams, which is decidedly superior than that obtained by the known traffic signals of the static type, as above disclosed.
The multi-color traffic signal according to the invention is characterized by the fundamental feature that the light conducting system, or optical channel system, comprises at least one dichroic mirror which is spectrophotometrically adjusted with respect to the bands of wave length of the colored lights produced by the individual projector units, each dichroic mirror being arranged, at the interior of the optical channel system, in such a manner as to reflect towards the irradiating output optics the colored light beam produced by a projector unit associated thereto, while it permits the passage towards the said irradiating output unit of the colored light beams produced by the remaining projector units.
More particularly, the traffic signal for railways with the possibility of selectively projecting one of three colored lights (green, red and yellow) comprises for each color a projector unit consisting of a lamp, an optical unit and a chromatic filter. The projector units are connected to an irradiating output optics by means of an optical channel system consisting of a main rectilinear channel presenting at one end the irradiating output optics and at the other end a first projector unit in axial alignment with the main channel. A second and third projector units are housed in transverse channels at 90.degree. with respect to the main channel and open thereinto. A first dichroic mirror is arranged in the main channel with an angle of 45.degree. in correspondence with the outlet of the transverse channel of the second projector unit and a second dichroic mirror is arranged in the main channel with an angle of 45.degree. in correspondence with the outlet of the transverse channel of the third projector unit.
The above and other features of the invention and the resulting advantages, will be understood from the following detailed description of a preferred embodiment of same, given as non restrictive example, with reference to the attached drawing.